Although they were 2 weeks later than promised and they made a couple of mistakes on sizes, we were very impressed with the workmanship of the installers and would recommend them to anybody. Just carefully check your order and call them to follow up on deliver.

I have used Gem Windows and Doors for two sets of installations over approximately 5 years. I got great service when Spiros himself was working with me, but the salesperson in the office that I got transferred to for the second set of windows was slow to respond and didn't seem to care about my project.
The main grievance I had with the sales people is that they suggested and installed awning windows on my second-floor and there is no way to clean them. I would have expected them to strongly suggest sliders...when I said something to them about this they didn't suggest any alternatives (or compensation for their bad advice).
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The installers however are great. The are professional, helpful and upfront about things. They cleaned up well and did the job in a short amount of time.

We hired Gem to install a patio door with a retractable screen door in our kitchen. The work on the installation was excellent, but the salesman (Seymour) was a complete loss. We pointed out a handle that we liked, but asked for one without a key-lock on the outside which he happily sold us. As it turns out, that style only comes with a key-lock. Even at that, they didn't have the right handle when they came to install the first time, so they had to come back when it finally came in.

We also had problems with the quality of the retractable screen. The one in the showroom was very sturdy and had protective tape at the top and bottom of the screen, and that is what we pointed to when we ordered one. The one they installed was a different style, with a tendency to twist when you open/close it and with no protective tape, so I expect the screen will start to fray before long as it occasionally gets pulled out of the track.

When we complained about this, Seymour's attitude was very condescending and rude. He wouldn't return phone calls, or get back to us when he said he would, ever, so I kept having to go back down to the store to try and get him to correct the situation. Every time he'd find some new excuse and say he'd look into it and get back to us, and he never did. Eventually the screen door was replaced (due to a minor flaw) with the exact same model, but slightly sturdier, so we decided to take it as a learning experience. They got our money on this deal, but we've got more doors and windows to replace next year, and they won't be seeing another cent from us.

They have a showroom in the westend of Toronto and it's good to check that out first. They replaced all our windows with energy-efficient windows and the total cost was $6,000. We are pleased with the windows and the service since it has been installed 2 years ago.

We have already referred Gem to a relative looking for parts for their casement window.

Jim at Gem is a very helpful, knowledgeable and approachable guy, apparently the only person in charge of and with access to the parts department. Be sure to phone ahead to make sure he is there to save yourself a trip.

We bought replacement parts for two casement windows and the replacement lock part for a sliding door. Jim readily explained and willingly demonstrated, using a window on display in the store, how to properly and easily (yet to be seen!) install the window parts.

The price was reasonable, too, compared to the prices I saw at a leading box store with similar but not the correct hardware we needed.